The present invention relates to an automobile antenna apparatus which is adaptable to an intelligent transportation system (referred to as ITS hereinafter) in its optimum condition.
FIG. 22 is a conceptual illustration of both ITS environment which can be considered to be almost ideal at the present time and the current automotive technologies (e.g., vehicle-mounted information communication technologies) which are arranged so as to be in harmony with the ITS environment.
As illustrated in FIG. 22, an automobile 310 running on an expressway 300 in the ITS environment, is required to have as many functions as possible, such as a radio receiving function 001 of receiving broadcast waves from an AM/FM radio broadcast station 301, a TV receiving function 002 of receiving broadcast waves from a TV broadcast station 302, a GPS receiving function 003 of receiving GPS waves from a GPS satellite 303, a transmitting/receiving function 004 of transmitting/receiving satellite communications and broadcast waves relayed by a communications satellite 304, a mobile communications function 005 for transmitting/receiving waves of a car phone and e-mail via a base station 305, a digital broadcast receiving function 006 for receiving digital broadcast waves, which mainly provides traffic information service and DGPS (differential global positioning service), from a digital broadcast station 306, an information exchange function 007 for exchanging information on the use of an electric toll collection (ETC) system with an automatic tollgate 307, and an anti-collision function 008 using an EHF (extremely high frequency) radar 308 mounted on the automobile 310.
The automobile 310 has to be equipped with an automobile antenna apparatus in order to fulfill the above functions. It also has to have artificial intelligence 009A including various types of sensors and high-performance microcomputers for recognition and its corresponding automatic control and a basic function 009B for controlling an operation such as running, communications, accident prevention, and car navigation.
FIG. 23 is a sketch of a prior art automobile antenna apparatus having the foregoing functions. As shown in FIG. 23, all of an AM/FM receiving antenna 311, two TV receiving antennas 312 and 312', two GPS receiving antennas 313 and 313', an automobile phone antenna 315, and an anti-collision EHF radar antenna 318 (a Mills cross compound antenna) are dispersed on the body of the automobile 310 in order to be adaptable to the media.
FIGS. 24A to 24C illustrate a concrete constitution of an anti-collision EHF radar 308 including the above radar antenna 318. FIG. 24A is a partly-broken view of the layout of the EHF radar 308, FIG. 24B is an illustration of the circuit arrangement thereof, and FIG. 24C is an illustration of a composite antenna beam 330 emitted from the radar antenna 318.
In FIGS. 24A and 24B, reference numeral 318a denotes a transmitting antenna element, and numeral 318b does a receiving antenna element. These antenna elements 318a and 318b constitute the anti-collision EHF radar antenna 318. Numeral 320 indicates a 60-GHz-EHF-wave generator including a gun oscillator 321, a circulator 322, a directional coupler 323, and a mixer 324. If the EHF radar 308 is activated, as shown in FIG. 24C, the composite antenna beam 330 is emitted from the anti-collision EHF radar antenna 318.
The direction (antenna directivity) of beams emitted from the antennas 311 to 314 in the prior art automobile antenna apparatus shown in FIG. 23, is set in advance to a fixed one in the early stage of use. If, therefore, the antenna directivity is not align with the direction of incoming waves, not only the optimum reception cannot be performed but also noise would be caused by a so-called multipass.
Since usually the emission range of the composite antenna beam 330 emitted from the radar antenna 318 shown in FIGS. 24A to 24C, is fixed, an obstruction can be detected only in a specific range in front of the body of the automobile 310. For this reason, the conventional anti-collision EHF radar 308 is very low in its obstruction detection capability, for example, at a curve in a road and thus it has been desired that the radar should be improved.